High ambient heat combined with a charging device’s own heat output raises the risk of thermal throttling or triggering a protective slowdown.
For a phone, the practical impact of summer conditions shows up mainly as slower charging speed and, in extreme conditions, a temporary charging pause as a protective measure — not permanent damage in normal use.
What to do
Let a phone that’s been in extreme heat or cold acclimate for a few minutes before charging at full speed — most protective slowdowns resolve on their own once the device or battery reaches a safer temperature range.